The molecular events that underlie the cell-surface stimulatory activity of membrane-active agents are purported to involve changes in membrane phospholipids as well as alterations in calcium (Ca2 ion) availability. An important biochemical event in drug-membrane perturbations is thought to be the activation of phospholipase A2 (PLA2) which cleaves arachidonic acid from position-2 of the phospholipid. If PLA2 plays a primary role in membrane-excitation phenomena, then this enzyme could be a primary locus of Ca2 ion action, since Ca2 ion is essential for nonlysosomal PLA2 activity. We have previously demonstrated an ACTH-induced turnover of arachidonyl phosphatidylinositol, which is temporally and quantitatively linked to ACTH-induced activation of steroid release. Preliminary studies point to a similar Ca2 ion-dependent deacylation-reacylation system in the rabbit neutrophil. We propose to extend our investigations to the pancreatic acinar cell in order to uncover salient information regarding the Ca2 ion-dependent events which underlie the regulation of exocrine secretory function. Phospholipid turnover and prostaglandin (PG) production will be monitored in rat acinar cell suspensions and in homogenates of acinar tissue by thin layer and high performance liquid chromatography. Amylase release will be determined by spectrophotometry and cyclic nucleotides by radioimmunoassay. Enzyme assays for guanylate cyclase and PLA2 will be carried out. We will probe the effects of pancreatic secretagogues on PLA2 activation, on radiolabeled arachidonate incorporation into phospholipids, and on PG production. The role of Ca2 ion in these events will be examined. Temporal and quantitative comparisons will be made between the turnover of arachidonic acid (and other precursors) in various phospholipids and amylase secretion. The relation between these events and activation of guanylate cyclase will also be assessed. These studies should help to define the role of Ca2 ion in the membrane events associated with exocrine secretion; they should afford us a better understanding of the pathophysiological processes associated with cystic fibrosis.